#import "lib/unify.typ": qty, qtyrange #import "@preview/cetz:0.5.2" = Mechanical specifications == Modules === Cassette ==== Shielding and construction To achieve metrologic tier precision, modules must be fully shielded from external interference. The only entry points for noise are: - The DB-25 and BNC connectors at the rear, which connects via a shielded cable to the power distribution board - The banana jacks at the front panel, which include input protection circuits. Modules must also not pollute neighboring modules with internally generated noise (such as PWAM oscillators). For this reason, all modules are enclosed in individual steel cassettes. We chose steel instead of aluminum, as it has better shielding properties, especially in terms of magnetic shielding. #figure( table( columns: 2, table.header([Parameter], [Value]), [Material], [DC01 cold-rolled steel (EN 10130)], [Thickness], [$qty(1.2, "mm")$], [Finish], [Matte black powder coard (RAL 9005), all surfaces.], ), caption: [Cassette construction parameters], ) ==== External dimensions #figure( cetz.canvas({ import cetz.draw: * // Scale factor: 1 mm = 0.035 drawing units let s = 0.035 let h-panel = 177.8 * s // 6.223 let h-body = 165.1 * s // 5.7785 let h-lip = 6.35 * s // 0.22225 let w-panel = 38.0 * s // 1.33 let d-body = 152.4 * s // 5.334 let t-panel = 3.0 * s // 0.105 (exaggerated slightly for visual clarity) let y-center = 0 let y-top-panel = h-panel / 2 let y-bot-panel = -h-panel / 2 let y-top-body = h-body / 2 let y-bot-body = -h-body / 2 // --- FRONT ELEVATION --- let x-front-left = 0 let x-front-right = w-panel let x-front-mid = w-panel / 2 // View Title content((x-front-mid, y-top-panel + 0.8), text( size: 9pt, weight: "bold", )[FRONT ELEVATION]) // Front Panel Outline rect( (x-front-left, y-bot-panel), (x-front-right, y-top-panel), fill: luma(250), stroke: 1.2pt + black, ) // Hidden Body Transition Lines (Dashed) line( (x-front-left, y-top-body), (x-front-right, y-top-body), stroke: (paint: luma(130), thickness: 0.7pt, dash: "dashed"), ) line( (x-front-left, y-bot-body), (x-front-right, y-bot-body), stroke: (paint: luma(130), thickness: 0.7pt, dash: "dashed"), ) // Panel Mounting Screw Holes (Top and Bottom Lips) circle( (x-front-mid, y-top-panel - h-lip / 2), radius: 0.08, fill: white, stroke: 0.8pt + black, ) circle( (x-front-mid, y-bot-panel + h-lip / 2), radius: 0.08, fill: white, stroke: 0.8pt + black, ) // Dimension: Panel Width (38.0 mm) line( (x-front-left, y-bot-panel), (x-front-left, y-bot-panel - 0.6), stroke: 0.5pt + luma(120), ) line( (x-front-right, y-bot-panel), (x-front-right, y-bot-panel - 0.6), stroke: 0.5pt + luma(120), ) line( (x-front-left, y-bot-panel - 0.6), (x-front-right, y-bot-panel - 0.6), mark: (start: "stealth", end: "stealth"), mark-size: 0.12, stroke: 0.7pt + black, ) content((x-front-mid, y-bot-panel - 0.9), text( size: 7.5pt, )[$qty(38.0, "mm")$]) // Dimension: Panel Height (177.8 mm / 4U) line( (x-front-left, y-top-panel), (x-front-left - 0.6, y-top-panel), stroke: 0.5pt + luma(120), ) line( (x-front-left, y-bot-panel), (x-front-left - 0.6, y-bot-panel), stroke: 0.5pt + luma(120), ) line( (x-front-left - 0.6, y-bot-panel), (x-front-left - 0.6, y-top-panel), mark: (start: "stealth", end: "stealth"), mark-size: 0.12, stroke: 0.7pt + black, ) content( (x-front-left - 0.95, y-center), text(size: 7.5pt)[$qty(177.8, "mm")$ ($qty(4, "U")$)], angle: 90deg, ) // --- SIDE ELEVATION --- let x-side-start = 2.8 let x-panel-back = x-side-start + t-panel let x-body-rear = x-panel-back + d-body let x-side-mid = (x-side-start + x-body-rear) / 2 // View Title content((x-side-mid, y-top-panel + 0.8), text( size: 9pt, weight: "bold", )[SIDE ELEVATION]) // Cassette Steel Body rect( (x-panel-back, y-bot-body), (x-body-rear, y-top-body), fill: luma(235), stroke: 1.2pt + black, ) // Front Panel Plate Attached to Body rect( (x-side-start, y-bot-panel), (x-panel-back, y-top-panel), fill: luma(210), stroke: 1.2pt + black, ) // Rear DB-25 Connector Standoff / Bezel Projection rect( (x-body-rear, y-center - 0.6), (x-body-rear + 0.25, y-center + 0.6), fill: luma(240), stroke: 0.8pt + black, ) // Dimension: Depth (152.4 mm) line( (x-panel-back, y-top-panel), (x-panel-back, y-top-panel + 0.2), stroke: 0.5pt + luma(120), ) line( (x-body-rear, y-top-panel - 0.2), (x-body-rear, y-top-panel + 0.2), stroke: 0.5pt + luma(120), ) line( (x-panel-back, y-top-panel + 0.2), (x-body-rear, y-top-panel + 0.2), mark: (start: "stealth", end: "stealth"), mark-size: 0.12, stroke: 0.7pt + black, ) content(((x-panel-back + x-body-rear) / 2, y-top-panel + 0.4), text( size: 7.5pt, )[$qty(152.4, "mm")$]) // Dimension: Body Height (165.1 mm) line( (x-body-rear, y-top-body), (x-body-rear + 0.6, y-top-body), stroke: 0.5pt + luma(120), ) line( (x-body-rear, y-bot-body), (x-body-rear + 0.6, y-bot-body), stroke: 0.5pt + luma(120), ) line( (x-body-rear + 0.6, y-bot-body), (x-body-rear + 0.6, y-top-body), mark: (start: "stealth", end: "stealth"), mark-size: 0.12, stroke: 0.7pt + black, ) content( (x-body-rear + 0.9, y-center), text(size: 7.5pt)[$qty(165.1, "mm")$], angle: -90deg, ) // Dimension: Top Lip Height (6.35 mm) line( (x-panel-back, y-top-panel), (x-body-rear + 1.8, y-top-panel), stroke: 0.4pt + luma(160), ) line( (x-panel-back, y-top-body), (x-body-rear + 1.8, y-top-body), stroke: 0.4pt + luma(160), ) line( (x-body-rear + 1.65, y-top-body), (x-body-rear + 1.65, y-top-panel), mark: (start: "stealth", end: "stealth"), mark-size: 0.10, stroke: 0.7pt + black, ) content( (x-body-rear + 2.2, (y-top-panel + y-top-body) / 2), text(size: 7.0pt)[$qty(6.35, "mm")$], ) }), caption: [Cassette enclosure orthographic projections (front and side elevation) detailing external physical dimensions and lip offsets.], ) #figure( table( columns: 4, table.header([Dimension], [Value], [Tolerance], [Note]), [Panel height], [$qty(177.8, "mm")$ ($qty(4, "U"), qty(7, "inch")$)], [$plus.minus qty(0.1, "mm")$], [Full rack unit height], [Grid pitch], [$qty(38.1, "mm")$ ($qty(1.5, "inch")$)], [N/A], [Theoretical center to center spacing. Two columns of banana jacks ($qty(0.75, "inch")$ grid).], [Panel Width], [$qty(38.0, "mm")$ ($qty(1.5, "inch")$)], [$+0.0 "/" -0.1 "mm"$], [Undersized to accomodate paint thickness and thermal expansion.], [Body height], [$qty(165.1, "mm")$, ($qty(6.5, "inch")$)], [$plus.minus qty(0.1, "mm")$], [Fits between rails], [Body width], [$qty(38.0, "mm")$ ($qty(1.5, "inch")$)], [$+0.0 "/" -0.1 "mm"$], [Same as panel], [Depth], [$qty(152.4, "mm")$ ($qty(6, "inch")$)], [$plus.minus qty(0.2, "mm")$], [Front to rear], [Lip height], [$qty(6.35, "mm")$ ($qty(0.25, "inch")$)], [N/A], [Top and bottom], ), caption: [Cassette external dimensions], ) The panel lips extend above and below the cassette body to fill the full $qty(4, "U")$ rack opening while the body fits between the chassis rails. ==== Construction The cassette consists of the front panel, one L-shaped steel channel and one interlocking U-shaped steel channel: ===== L-channel (chassis) #figure( image("pictures/l-channel.svg"), caption: [L-channel (chassis) construction], ) / Role: Structural spine. Holds the PCB and Front Panel. / Geometry: / Left wall ($qty(165.1, "mm") times qty(152.4, "mm")$): PCB mounts here. / Rear closure ($qty(165.1, "mm") times qty(35.7, "mm")$): Includes DB-25 and BNC cutouts. / DB-25 cutout: Center X: $qty(17.85, "mm")$ (centered). Center Y: $qty(55.0, "mm")$ from bottom edge. / BNC cutout: Center X: $qty(17.85, "mm")$ (centered). Center Y: $qty(130.0, "mm")$ from bottom edge. / Facultative: Required only for modules utilizing the Master Oscillator. If absent, the steel surface remains solid to maintain maximum shielding integrity. / Flanges (The Mounting Points): - The Left Wall features Top, Bottom and Front flanges folded $qty(90, "degree")$ inward. - The Rear Wall features Top, Bottom, and Right flanges folde $qty(90, "degree")$ inward. - The flanges are $qty(8, "mm")$. / Threads: These flanges must be fitted with M3 Press-Fit Threaded Inserts (PEM Nuts) or similar clinching fasteners. / Why: The $qty(1.2, "mm")$ steel is too thin to tap reliably for repeated use. Inserts ensure the threads don't strip after years of maintenance. / Finish: The outer face of these flanges must be masked (unpainted) to ensure electrical contact with the U-Channel and the front panel. ===== U-channel (cover) #figure( image("pictures/u-channel.svg"), caption: [U-channel (cover) construction], ) / Role: EMI Shielding and Protection. / Geometry: / Top ($qty(35.7, "mm") times qty(152.4, "mm")$): vented / Right side wall ($qty(165.1, "mm") times qty(152.4, "mm")$): / Bottom ($qty(35.7, "mm") times qty(152.4, "mm")$): vented / Holes: Features Countersunk Through-Holes corresponding to the L-Channel's threaded inserts. / Finish: The inner face contact area must be masked (unpainted). ===== Front panel #figure( image("pictures/front-panel-geometry.svg"), caption: [Front channel construction], ) / Geometry: $qty(177.8, "mm") times qty(38.0, "mm")$, body section $qty(165.1, "mm")$ / Holes: Features Countersunk Through-Holes corresponding to the L-Channel's threaded inserts. / Finish: The inner face contact area must be masked (unpainted). ===== Fasteners / Type: M3 Countersunk (Flat Head) Screws (Black Oxide). / Flushness: Screw heads must sit flush with the external surface to prevent snagging when sliding the module into the rack. / Spacing: Screws should be spaced no more than $qty(40, "mm")$ apart along the seams to ensure the "slot antenna" effect does not compromise shielding at high frequencies ($gt qty(1, "GHz")$). There are $5$ screws per vertical flange, seam, and $4$ per horizontal seam. ===== Grounding requirements To prevent the cassette from acting as a floating antenna, the enclosure must maintain a low-impedance electrical connection to the chassis earth. The connection is made at the DB-25 port and the rear BNC connector shell if present. The mounting holes must be masked during powder coating, or star washers be used to screw it in place. The BNC connector shell must be bonded to the steel cassette (masking required). The signal carried by the BNC (10MHz) is referenced to the BNC shell (Chassis Earth/RF Ground), not AGND, to prevent high-frequency injection into the precision analog ground plane. To ensure the connections actually block noise (RF), masking is mandatory: The powder coat is an insulator. There must be masking (no paint) on the outer face of all L-Channel flanges and the corresponding inner face of the U-Channel and Panel. When the screws are tightened, metal-to-metal contact must be achieved around the entire perimeter of the seam. If paint blocks this contact, the shielding will fail, degrading the SNR below the $qty(90, "dB")$ target. ==== Internal dimensions #figure( table( columns: 2, table.header([Dimension], [Value]), [Height], [$qty(162.7, "mm")$], [Width], [$qty(35.6, "mm")$], [Depth], [$qty(150, "mm")$], ), caption: [Cassette internal dimensions], ) ==== Ventilation Top and bottom faces include ventilation slots for convective cooling while maintaining EMI shielding. #figure( image("pictures/ventilation.svg"), caption: [Cassette ventilation], ) #figure( table( columns: 2, table.header([Parameter], [Value]), [Slot size], [$qty(2.5, "mm") times qty(10, "mm")$], [Slot orientation], [Length parallel to cassette depth], [Rows], [$5$], [Row pitch], [$qty(5, "mm")$], [Columns], [$12$], [Column pitch], [$qty(12, "mm")$], [Slots per face], [$60$], [Open area], [$approx qty(28, "percent")$], [Shielding effectiveness], [$gt qty(20, "dB") "to" qty(1, "GHz")$], ), caption: [Cassette ventilation specifications], ) ==== DB-25 connector cutout #figure( image("pictures/db-25-connector-cutout.svg"), caption: [DB-25 connector cutout], ) #figure( table( columns: 2, table.header([Parameter], [Value]), [Shape], [D-shaped (standard DB-25 profile)], [D-opening width], [$qty(33.3, "mm")$], [D-opening height], [$qty(12.5, "mm")$], [Mounting hole spacing], [$qty(24.99, "mm")$], [Mounting hole size], [$diameter qty(3.2, "mm")$], [Center X], [$qty(17.85, "mm")$ from either edge], [Center Y], [$qty(82.5, "mm")$ from top/bottom (centered on $qty(165.1, "mm")$)], [Connector assembly], [Panel mount with solder cups], [Position], [Centered on rear closure], ), caption: [Cassette DB-25 connector cutout specifications], ) ==== PCB dimensions The PCB is sized to fit within the L-Channel side wall while leaving clearance for the interlocking U-Channel flanges and internal cabling. / PCB Height: $qty(155.0, "mm")$ / PCB Depth: $qty(125.0, "mm")$ / PCB Thickness: $qty(1.6, "mm")$ (Standard FR-4) / Orientation: Mounted vertically on the internal Left Wall. ===== PCB mounting geometry The cassette Left Wall shall feature four ($4$) permanently attached female threaded standoffs (M3) to accept the PCB. / Standoff Type: M3 Thread, 6mm Height (swaged or welded to the steel wall). / Mounting Pattern: Rectangular, centered on the cassette side wall. / Vertical Spacing (Y): $qty(135.0, "mm")$ / Horizontal Spacing (X): $qty(105.0, "mm")$ / Origin Reference: Pattern is centered relative to the internal side wall dimensions ($qty(165.1, "mm") times qty(150, "mm")$). ===== Keep-out zones To prevent electrical shorts against the steel chassis or mechanical interference: / Perimeter Clearance: A 5mm component-free zone must be maintained along all four edges of the PCB. / Height Clearance: Components taller than 30mm are prohibited to ensure airflow and prevent shorting against the opposing Right Wall (total internal width is $qty(35.7, "mm")$. If tall components must be used, they must be assembled parallel to the PCB. ===== Interconnect layout (wire harness strategy) Since the DB-25 is panel-mounted with solder cups and controls are on the front panel, the PCB layout must optimize cable routing to minimize noise pickup and maximize air flow. / Zone A (Rear - Power): / Function: Connection to the rear DB-25 backplane connector. / Location: Rear $qty(20, "mm")$ of the PCB. / Connector Type: Pluggable terminal block (e.g., Phoenix Contact $qty(3.5, "mm")$) or latching header (e.g., Molex KK $qty(3.96, "mm")$). Direct soldering of flying leads to the PCB is discouraged to maintain repairability. / Pinout: Must match the standard SAME Power Distribution definition. / Zone B (Front - I/O): / Function: Connection to Front Panel Banana Jacks and Potentiometers. / Location: Front $qty(20, "mm")$ of the PCB. / Routing: Cables should form a neat loom transitioning from the PCB edge to the panel components. / Service Loop: All internal cabling must have a service loop of $plus qty(20, "mm")$ to allow the PCB to be unscrewed and slightly lifted without desoldering. ===== Grounding & Isolation Strategy To maintain the strict separation of Analog Ground (AGND) and Chassis Earth, the PCB must be electrically isolated from the steel cassette. / PCB Mounting Holes: Must be unplated and isolated from all internal ground planes (AGND/DGND). The metal standoffs serve only as mechanical support, not electrical conductors for the circuit. / Cassette Earth Path: The steel cassette connects to Chassis Earth exclusively via the rear DB-25 Connector. / Implementation: The DB-25 panel-mount connector must have a conductive metal shell. When mounted to the rear steel panel, the connector shell (and Pin $25$) creates the bond between the cable shield and the cassette body. / Verification: Resistance between the DB-25 Shell and any point on the cassette powder-coat-free zones must be $lt qty(0.1, "ohm")$. === PCB ==== Overview Module PCBs mount vertically within the L-channel, attached to the left side wall via standoffs. The PCB connects to the front panel (banana jacks, controls) via wire harnesses and to the power distribution board via the rear DB-25 connector. ==== Standard dimensions #figure( table( columns: 4, table.header([Parameter], [Value], [Tolerances], [Notes]), [Height], [$qty(155.0, "mm")$], [$plus.minus qty(0.2, "mm")$], [Vertical dimension when mounted], [Depth], [$qty(125.0, "mm")$], [$plus.minus qty(0.2, "mm")$], [Front-to-rear dimension], [Thickness], [$qty(1.6, "mm")$], [$plus.minus qty(0.15, "mm")$], [Standard 4-layer stackup], [Corner radius], [$qty(3.0, "mm")$], [$plus.minus qty(0.5, "mm")$], [All four corners, for insertion clearance], ), caption: [PCB standard dimensions], ) ==== Board stackup All SAME module PCBs shall use a 4-layer stackup: This allows proper ground management, while remaining easy to solder with standard equipment. #figure( table( columns: 4, table.header([Layer], [Function], [Copper weight], [Notes]), [L1 (top)], [Signal + components], [$qty(1, "oz")$ ($qty(35, "um")$)], [Component side faces right (toward U-channel)], [L2 (inner 1)], [Ground plane], [$qty(1, "oz")$ ($qty(35, "um")$)], [Continuous AGND plane, split for DGND if needed], [L3 (inner 2)], [Power plane], [$qty(1, "oz")$ ($qty(35, "um")$)], [Split for $plus.minus qty(15, "V")$, $plus.minus qty(5, "V")$ rails], [L4 (bottom)], [Signal + earth ring], [$qty(1, "oz")$ ($qty(35, "um")$)], [Faces left wall (mounting side), digital traces if needed], ), caption: [PCB board stackup], ) / Dielectric: FR-4, $"Tg" gt.eq qty(135, "dC")$ ==== Surface finish #figure( table( columns: 2, table.header([Parameter], [Specification]), [Finish], [ENIG (Electroless Nickel Immersion Gold)], [Nickel thickness], [$qtyrange(3, 5, "um")$], [Gold thickness], [$qtyrange(0.05, 0.1, "um")$ ($qtyrange(1, 2, "micro inch")$)], [Solder mask], [Matte black (both sides)], [Silkscreen], [White (both sides)], ), caption: [PCB surface finish], ) ===== Rationale ENIG provides excellent corrosion resistance for the 50-year service life target. A flat surface ensures reliable soldering of precision components. Gold does not oxidize, maintaining consistent contact resistance at test points. Black solder mask reduces light reflectivity (some precision semiconductors are photosensitive). ==== Earth ring The PCB shall include a Chassis Earth ring around the perimeter of the bottom layer (L4). This ring provides a defined path for any capacitively-coupled noise to drain to chassis earth rather than coupling into signal traces. ===== Geometry #figure( table( columns: 3, table.header([Parameter], [Value], [Notes]), [Width], [$qty(3.0, "mm")$], [Continuous copper pour], [Clearance from edge], [$qty(0.5, "mm")$], [Manufacturing tolerance], [Clearance to inner circuitry], [$qty(2.0, "mm")$], [Isolation gap], [Layer], [L4 (bottom) only], [Faces mounting wall], ), caption: [PCB earth ring geometry], ) ===== Connection The earth ring shall not connect to AGND or DGND on the PCB. It connects to Chassis Earth exclusively through the pin 25 of the DB-25 power distributor via a trace on L4. ===== Mounting holes details The four mounting holes shall be: - Unplated, isolated through-holes, $diameter qty(3.2, "mm")$ (M3 clearance). - Not connected to any layer (no vias to L1, L2, L3, L4). ==== Ground planes ===== AGND plane #figure( table( columns: 2, table.header([Parameter], [Value]), [Layer], [L2 (inner 1)], [Coverage], [Minimum $qty(85, "percent")$ of signal area], [Splits], [Only if DGND zone required], [Connection], [Via stitching to AGND traces & pads on L1 and L4], ), caption: [PCB AGND plane], ) The AGND plane provides: - Low-impedance return path for analog signals, - Shielding between signal layers, - Thermal spreading. ===== DGND zone (if needed) #figure( table( columns: 2, table.header([Parameter], [Value]), [Location], [Defined zone on L2], [Separation], [$qty(2, "mm")$ gap from AGND plane], [Connection], [To the DGND pins of the power distributor], [Via stitching], [Only within DGND zone], ), caption: [PCB DGND zone], ) ==== Power planes Layer 3 is divided into power distribution zones: #figure( table( columns: 3, table.header([Zone], [Rail], [Typical area]), [Zone 1], [$plus qty(15, "V")$], [$qtyrange(30, 40, "percent")$], [Zone 2], [$qty(-15, "V")$], [$qtyrange(30, 40, "percent")$], [Zone 3], [$plus qty(5, "V")$ (if needed)], [$qtyrange(10, 15, "percent")$], [Zone 4], [$qty(-5, "V")$ (if needed)], [$qtyrange(10, 15, "percent")$], ), caption: [PCB power planes], ) Design rules: - Miminum $qty(2, "mm")$ clearance between power zones, - Star distribution from power enty point, - Bulk decoupling capacitors from power enty point, - Local decoupling at each IC. ==== Mounting strategy The PCB mounts to the L-channel left wall via four standoffs. #figure( table( columns: 2, table.header([Parameter], [Value]), [Standoff thread], [$M 3$], [Standoff height], [$qty(6, "mm")$], [Standoff type], [Female threaded, swaged or welded to L-channel], [Mounting screw], [$M 3 times qty(8, "mm")$ pan head], ), caption: [PCB mounting strategy: standoffs], ) ===== Mounting holes pattern #figure( table( columns: 2, table.header([Parameter], [Value]), [Pattern], [Rectangular, $4$ holes], [Horizontal spacing (X)], [$qty(105.0, "mm")$], [Vertical spacing (Y)], [$qty(155.0, "mm")$], [Hole diameter], [$diameter qty(3.2, "mm")$ ($M 3$ clearance)], [Hole plating], [Unplated, isolated], ), caption: [PCB mounting strategy: mounting holes], ) ====== Positions #figure( table( columns: 3, table.header([Hole], [X], [Y]), [1 (bottom-left)], [$qty(10.00, "mm")$], [$qty(10.00, "mm")$], [2 (bottom-right)], [$qty(115.00, "mm")$], [$qty(10.00, "mm")$], [3 (top-left)], [$qty(10.00, "mm")$], [$qty(145.00, "mm")$], [4 (top-right)], [$qty(115.00, "mm")$], [$qty(145.00, "mm")$], ), caption: [PCB mounting strategy: mounting holes positions], ) ==== Keep-out zones ===== Perimeter keep-out #figure( table( columns: 3, table.header([Parameter], [Value], [Notes]), [Width], [$qty(5.0, "mm")$], [All four edges], [Applies to], [Components and tall traces], [Solder mask and silkscreen allowed], [Reason], [Clearance for cassette walls and earth ring], [], ), caption: [PCB keep-out zones: perimeter keep-out], ) ===== Mounting holes keep-out #figure( table( columns: 2, table.header([Parameter], [Value]), [Radius], [$qty(0.5, "mm")$ from hole center], [Applies to], [Components, traces, planes (except earth ring)], ), caption: [PCB keep-out zones: mounting holes keep-out], ) ==== Interconnect zones ===== Zone A: power and master oscillator entry (rear) #figure( table( columns: 2, table.header([Parameter], [Value]), [Location], [Rear $qty(20, "mm")$ of PCB ($Y = qtyrange(0, 20, "mm")$)], [Function], [Connection to DB-25 backplane connector and rear BNC], [Connector], [ / Power: pluggable terminal block (e.g. Phoenix Contact MSTB $qty(3.5, "mm")$ or latching header (e.g Molex KK $qty(3.96, "mm")$). / Master oscillator (optional): The rear BNC connects to the PCB via a short ($lt qty(50, "mm")$) $qty(50, "ohm")$ coaxial pigtail (RG-174 or RG-316) soldered to dedicated RF pads or a u.FL/SMA connector on the PCB edge. ], [Wire gauge], [$qtyrange(22, 24, "AWG")$ for power, $qty(26, "AWG")$ for signals], ), caption: [PCB interconnect zones: zone A], ) ====== Pin assignment The PCB connector shall provide access to all power rails in a logical grouping: #figure( table( columns: 3, table.header([Position], [Signal], [Recommended wire color]), [1], [$plus qty(15, "V")$], [Red], [2], [$qty(-15, "V")$], [Orange], [3], [AGND], [Black], [4], [$plus qty(10, "V")$ force], [White], [5], [$plus qty(10, "V")$ sense], [White / red stripe], [6], [$qty(-10, "V")$ force], [Grey], [7], [$qty(-10, "V")$ sense], [Gred / red stripe], [8], [$plus qty(5, "VD")$], [Yellow], [9], [$qty(-5, "VD")$], [Blue], [10], [DGND], [Brown], [11], [Stagger], [Purple], [12], [Chassis Earth], [Green / yellow stripe], ), caption: [PCB interconnect zones: zone A pin assignment], ) Not all modules require all signals. Unused positions may be omitted from the harness. ===== Zone B: front panel I/O #figure( table( columns: 2, table.header([Parameter], [Value]), [Location], [Front $qty(20, "mm")$ of PCB ($Y = qtyrange(135, 155, "mm")$)], [Function], [Connection to banana jacks and controls], [Connector], [Pin headers, terminal blocks, or direct solder pads], [Wire gauge], [$qtyrange(24, 25, "AWG")$], ), caption: [PCB interconnect zones: zone B], ) Design guidelines: - Group outputs on one side, inputs on the other, - Maintain signal flow from right to left (input #sym.arrow.r processing #sym.arrow.r output), - Include test points for each signal node. ===== Service loop requirements All internal wiring shall include a service loop of minimum $qty(20, "mm")$ additional length. This allows the PCB to be: - Unscrewed from standoffs, - Tilted or lifted for inspection, - Accessed for rework. Without disconnecting the wire harnesses. ==== Silkscreen requirements ===== Component side (L1 - top) #figure( table( columns: 2, table.header([Element], [Requirement]), [Reference designators], [All components labeled($R_"bias"$, $C_"bulk"$, $U_"buf"$, etc.)], [Polarity marks], [All polarized components (diodes, electrolytics, ICs, etc.)], [Pin 1 indicators], [All ICs and connectors], [Assembly notes], [Tier-specific component values (if applicable)], [Test points], [Labeled with signal name], ), caption: [PCB silkscreen requirements: component side (L1 - top)], ) Labels should be functional if possible, defaults to $R_1$, $C_1$, $U_1$, etc. if there are space constraints. ===== Solder side (L4 - bottom) #figure( table( columns: 2, table.header([Element], [Requirement]), [Board identification], [Module name, version, date], [SAME logo], [Mandatory], [Precision tier], ["$"EDU"$", "$"IND"$", or "$"MET"$" marking area], [Designer attribution], [Name, handle or logo], [License], ["$"CERN-OHL-S-2.0+"$"], ), caption: [PCB silkscreen requirements: solder side (L4 - bottom)], ) ==== Electrical testing All PCBs shall pass the following tests before assembly: #figure( table( columns: 2, table.header([Test], [Requirement]), [Isolation], [$gt qty(100, "mega ohm")$ between unconnected nets], [Continuity], [All nets per netlist], [Earth ring isolation], [$gt qty(100, "mega ohm")$ between earth ring and AGND/DGND], [Earth ring continuity], [$lt qty(1, "ohm")$ along entire earth ring perimeter (measure between opposite corners of the ring trace)], ), caption: [PCB electrical testing requirements], ) === Panels ==== Geometry The front panel is a separate piece that attaches to the L-channel via countersunk screws. #figure( table( columns: 3, table.header([Parameter], [Value], [Tolerance]), [Height], [$qty(177.8, "mm")$ ($qty(4, "U"), qty(7, "inch")$)], [$plus.minus qty(0.1, "mm")$], [Width], [$qty(38, "mm")$], [$plus 0.0 "/" qty(-0.1, "mm")$], [Thickness], [$qty(1.2, "mm")$], [$plus.minus qty(0.1, "mm")$], [Material], [DC01 cold-rolled steel], [N/A], [Finish], [Matte black powder coat (RAL 9005)], [N/A], ), caption: [Panels geometry], ) ===== Panels zones #figure( table( columns: 3, table.header([Zone], [Height range], [Function]), [Top lip], [$qtyrange(0, 6.35, "mm")$], [Extends above cassette body], [Body], [$qtyrange(6.35, 171.45, "mm")$], [Jack and control area], [Bottom lip], [$qtyrange(171.45, 177.8, "mm")$], [Extends below cassette body], ), caption: [Panels zones], ) ==== Grid All panel-mounted components follow a $qty(0.75, "inch")$ ($qty(19.05, "mm")$) grid for compatibility with standard banana jack spacing and shorting bars. #figure( image("pictures/grid.svg"), caption: [Grid], ) ===== Origin #figure( table( columns: 2, table.header([Parameter], [Value]), [Origin X], [$qty(9.525, "mm")$ from left edge (first column center)], [Origin Y], [$qty(22.225, "mm")$ from top edge (first row center)], [Column pitch], [$qty(19.95, "mm")$ ($qty(0.75, "inch")$)], [Row pitch], [$qty(19.95, "mm")$ ($qty(0.75, "inch")$)], [Columns], [$2$], [Rows], [$8$], ), caption: [Panels grid orign], ) ===== Positions #figure( table( columns: 5, table.header([Position], [Column], [Row], [X (from left)], [Y (from top)]), [A1], [$1$], [$1$], [$qty(9.525, "mm")$], [$qty(22.225, "mm")$], [B1], [$2$], [$1$], [$qty(28.575, "mm")$], [$qty(22.225, "mm")$], [A2], [$1$], [$2$], [$qty(9.525, "mm")$], [$qty(41.275, "mm")$], [B2], [$2$], [$2$], [$qty(28.575, "mm")$], [$qty(41.275, "mm")$], [A3], [$1$], [$3$], [$qty(9.525, "mm")$], [$qty(60.325, "mm")$], [B3], [$2$], [$3$], [$qty(28.575, "mm")$], [$qty(60.325, "mm")$], [A4], [$1$], [$4$], [$qty(9.525, "mm")$], [$qty(79.375, "mm")$], [B4], [$2$], [$4$], [$qty(28.575, "mm")$], [$qty(79.375, "mm")$], [A5], [$1$], [$5$], [$qty(9.525, "mm")$], [$qty(98.425, "mm")$], [B5], [$2$], [$5$], [$qty(28.575, "mm")$], [$qty(98.425, "mm")$], [A6], [$1$], [$6$], [$qty(9.525, "mm")$], [$qty(117.475, "mm")$], [B6], [$2$], [$6$], [$qty(28.575, "mm")$], [$qty(117.475, "mm")$], [A7], [$1$], [$7$], [$qty(9.525, "mm")$], [$qty(136.525, "mm")$], [B7], [$2$], [$7$], [$qty(28.575, "mm")$], [$qty(136.525, "mm")$], [A8], [$1$], [$8$], [$qty(9.525, "mm")$], [$qty(155.575, "mm")$], [B8], [$2$], [$8$], [$qty(28.575, "mm")$], [$qty(155.575, "mm")$], ), caption: [Panels grid positions], ) ===== Component placement rules #figure( table( columns: 3, table.header([Component], [Grid positions], [Hole size]), [$qty(4, "mm")$ banana jack], [Any], [$diameter qty(8.0, "mm")$], [$qty(6, "mm")$ potentiometer shaft], [Any], [$diameter qty(7.0, "mm")$], [$qty(3, "mm")$ LED], [Between grid positions], [$diameter qty(3.2, "mm")$], [Toggle switch], [Any], [Per switch specification], [Other components], [Centered on grid if possible], [Per component specification], ), caption: [Panels grid: component placement rules], ) ====== Off-grid placements + Small indicators (LEDs) and labels may be placed between grid positions. + Non-specified components (controls, interface ports, etc.) should be centered on grid positions if possible, or centered on the panel. + Mounting screws for the panel (into L-channel flanges) are outside the grid area. ==== Labelling All panels shall include clear, permanent labelling for user operation. #figure( table( columns: 3, table.header([Element], [Requirement], [Location]), [Module name], [Mandatory], [Top lip], [Module mathematical function], [Recommended, when applicable], [Above row $1$], [Jack function], [Mandatory], [Above or beside jack], [Jack type], [Mandatory, color-coded jack], [At jack], [Signal flow], [Recommended, arrows or grouping], [As needed], [License], [Mandatory], [Below row $8$], [Version and tier], [Mandatory], [Bottom lip], [Module designer name or logo], [Optional], [Bottom lip], [Module builder name or logo], [Optional], [Bottom lip], ), caption: [Panels labelling requirements], ) ===== Jacks color coding #figure( table( columns: 2, table.header([Jack color], [Signal type]), [White], [Input (bipolar)], [Light blue], [Output (bipolar)], [Light yellow], [Output (unipolar)], [Red], [Output (gate)], [Yellow], [Output (reference $plus qty(10, "V")$)], [Blue], [Output (reference $qty(-10, "V")$)], [Black], [Analog ground], ), caption: [Jacks color coding], ) ===== Use of colors in labels The panel has a matte black background. To maintain legibility, all labels should be white or off-white, with the following exceptions: - For the designer or builder name or logo. - When justified by the mathematical operation performed. In any case, colors should be designed to offer sufficient contrast, and not impact module usability by people suffering from color blindness. ===== Use of graphism and symbols in labels We recommend the use of mathematical symbols and graphism when they illustrate the functionality of the module. However, text labels should always be present to express the jack functions. ===== Label method Commercial, reference implementation or metrologic builds should always use laser engraving or screen printing methods. Those have excellent durability and legibility. DIY builds can use UV-printed vinyl overlay method: it maintains good durability and legibility while being more accessible. ===== Typography Labels should be printed in a sans-serif typeface (DIN 1451, Eurostile, Helvetica, etc.), except mathematical formulas. Module name size should be at least $qty(4, "mm")$ height. Jack labels should be at least $qty(2, "mm")$ height. == Chassis === Overview The chassis provides the mechanical and electrical infrastructure for housing modules. It includes: - Structural enclosure with EMI shielding, - Cassette rail system for module installation and removal, - Power distribution board with backplane connectors, - Front panel with reference outputs and system controls, - Thermal management provisions. This specification defines interface requirements that any compliant chassis must meet. Chassis may vary in capacity (number of module positions), form factor (rack-mount, desktop, portable), and mounting style. The reference implementation (@reference-implementation-chassis) describes a $qty(19, "inch")$ $qty(4, "U")$ rack-mount chassis with $8$ module positions. === Dimensional requirements #figure( image("pictures/chassis-module-loading.svg"), caption: [Chassis module loading dimensional requirements], ) ==== Module interface dimensions All chassis must accommodate standard SAME cassettes. The following dimensions are mandatory: #figure( table( columns: 3, table.header([Parameter], [Value], [Notes]), [Module pitch], [$qty(38.1, "mm")$ ($qty(1.5, "inch")$)], [Center-to-center spacing], [Module opening height], [$qty(177.8, "mm")$ ($qty(4, "U"), qty(7, "inch")$)], [Panel visible area], [Module body clearance], [$qty(165.2, "mm")$], [Between top and bottom rails], [Module depth], [$qty(152.5, "mm")$], [Front panel to rear connector], [Rail-to-rail width], [$qty(38.1, "mm")$ ($qty(1.5, "inch")$)], [Center-to-center spacing], ), caption: [Module interface dimensions], ) ==== Capacity Chassis capacity is defined by the number of module positions. There is no minimum or maximum, but the following constraints apply: #figure( table( columns: 3, table.header([Capacity], [Power budget], [Notes]), [Per module], [$qty(185, "mA") at plus.minus qty(15, "V")$], [Maximum per position], [Per module], [$qty(100, "mA") at plus.minus qty(5, "VD")$], [Maximum per position], [Total], [Scales with capacity], [Power distribution must support all positions], ), caption: [Chassis capacity power requirements], ) Designers should consider thermal dissipation when determining maximum capacity. ==== Clearances The rear clearance (behind cassette) should be at least $qty(25, "mm")$, to account for the DB-25 connector and cable bend radius. === Structural requirements ==== Material #figure( table( columns: 2, table.header([Parameter], [Requirement]), [Material], [Steel (recommended) or aluminum], [Minimum thickness], [$qty(1.5, "mm")$ (steel) or $qty(2.0, "mm")$ (aluminum)], [Finish], [Black powder coat or anodization, conductive areas masked], ), caption: [Chassis material requirements], ) Steel is preferred for magnetic shielding. Aluminum may be used where weight is critical, with reduced magnetic shielding performance. ==== EMI shielding A fully loaded chassis must form a continuous shielded enclosure: #figure( table( columns: 2, table.header([Parameter], [Requirement]), [Shielding effectiveness], [$gt qty(20, "dB"), qtyrange(80, 1000, "MHz")$], [Panel joints], [Metal-to-metal contact of conductive gasket], [Ventilation openings], [\ Maximum slot dimensions: $qty(10, "mm") times qty(2, "mm")$], [Cable entry], [Shield connectors or filtered feedthroughs], ), caption: [Chassis EMI shielding requirements], ) ==== Grounding #figure( table( columns: 2, table.header([Parameter], [Requirement]), [Chassis earth bonding], [All panels bonded to single earth point], [Earth impedance], [$gt qty(0.1, "ohm")$ between any two chassis points], [Safety earth], [Connected to mains earth via IEC inlet], [Module earth path], [Via DB-25 shell and pin 25], ), caption: [Chassis grounding requirements], ) === Cassette rails The rail system guides cassette insertion and provides retention. ==== Geometry #figure( table( columns: 3, table.header([Parameter], [Value], [Notes]), [Rail height], [$qty(6.35, "mm")$ ($qty(0.25, "inch")$)], [Matches cassette lip height], [Channel width], [$qty(38.1, "mm")$ ($qty(1.5, "inch")$) $plus 0.2 "/" minus qty(0.0, "mm")$], [Accepts cassette body with clearance], [Channel depth], [$qty(5, "mm")$ minimum], [Guides cassette during insertion], [Rail length], [Full chassis depth], [Front to rear], ), caption: [Chassis cassette rails geometry], ) ==== Retention Cassettes must be retained to prevent accidental ejection during operation or transport. #figure( table( columns: 2, table.header([Method], [Requirement]), [Friction fit], [Acceptable for stationary installations], [Positive retention], [Required for portable or vibration-prone environments], [Front panel screws], [Optional, into chassis front rail], ), caption: [Chassis cassette retention requirements], ) Positive retention may be achieved via: - Spring clips engaging cassette lips, - Latching mechanisms. ==== Material The rails must be of the same metal as the chassis, with a smooth, burr-free finish; and bond to chassis earth. They contribute to EMI shielding by closing the gap between cassette lips and chassis structure. === Thermal management ==== Cooling method Passive convection cooling is the baseline requirement. Forced-air cooling may be added for high-density configurations. #figure( table( columns: 2, table.header([Method], [Requirement]), [Passive (convection)], [Minimum for all chassis], [Active (forced air)], [Optional, for high-capacity or enclosed installations], ), caption: [Chassis cooling method requirements], ) ==== Ventilation Chassis ventilation must align with cassette ventilation slots to enable chimney-effect airflow. #figure( table( columns: 2, table.header([Parameter], [Requirement]), [Bottom ventilation], [Required, aligned with cassette bottom vents], [Top ventilation], [Required, aligned with cassette top vents], [Slot dimensions], [$lt.eq qty(10, "mm") times qty(2, "mm")$ for EMI compliance], [Open area], [$gt.eq qty(20, "percent")$ of cassette footprint area], ), caption: [Chassis ventilation requirements], ) ==== Thermal limits Inside the chassis cassette chamber, internal ambient temperature must not go over $qty(50, "dC")$. If passive cooling cannot maintain thermal limits at full capacity, forced-air cooling or reduced capacity is required. === Power distribution board The power distribution board generates and distributes all power rails to module positions. ==== Functions #figure( table( columns: 2, table.header([Function], [Requirement]), [AC-DC conversion], [Mains input to $plus.minus qty(15, "V")$, $plus.minus qty(5, "VD")$ rails. Can be external or internal], [Reference generation], [$plus.minus qty(10.0000, "V")$ precision references], [Master oscillator generation], [Generation of the $qty(10, "MHz")$ sine wave reference], [Distribution], [ - One female DB-25 connector per module position, - One female isolated BNC connector per module position ], [Calibration], [Front-panel accessible switches], [Protection], [Overcurrent, overvoltage, thermal shutdown], ), caption: [Power distribution board functional requirements], ) ==== Power entry #figure( table( columns: 2, table.header([Parameter], [Requirement]), [Mains connector], [IEC C14 (with integrated fuse) or regional equivalent], [Voltage range], [$qtyrange(100, 240, "VAC"), 50 "/" qty(60, "Hz")$ (universal) recommended. Factory setup accepted], [Safety], [Compliant with IEC 60950-1 or IEC 62368-1], ), caption: [Power entry requirements], ) ==== Master oscillator To support the metrologic tier time-domain computations, the chassis must include a precision clock source. / Oscillator: Oven Controlled Crystal Oscillator (OCXO). / Recommended part: AOCJY4A-10.0000MHZ-SW (or equivalent with $plus.minus qty(10, "ppb")$ stability). / Buffering: The oscillator output must be filtered to remove harmonics and buffered to drive the $qty(50, "ohm")$ distribution network. / Metrologic tier buffer: LM7171 (high speed, high voltage operational amplifier) or equivalent, configured to drive $qty(50, "ohm")$ loads with high slew rate and low distortion. / Signal level: $qty(1.0, "Vpp") plus.minus qty(10, "percent")$ into $qty(50, "ohm")$. / Waveform: Sine wave. / Fan-out: The oscillator distribution network must ensure port-to-port isolation $gt qty(40, "dB")$ to prevent oscillator line crosstalk between modules. === Front panel The chassis front panel provides system-level controls and reference inputs and outputs. ==== Elements #figure( table( columns: 3, table.header([Element], [Type], [Function]), [SAME logo], [Label], [N/A], [SAME license], [Label], [Legal], [Power switch], [Rocker or toggle], [Mains on/off], [Standby switch], [Toggle], [Maintains reference ovens temperature], [Power indicator], [LED], [Indicates power state], [Standby indicator], [LED], [Indicates standby state], [$plus qty(10.0000, "V")$ output jack], [4mm banana, yellow], [Reference voltage output], [$qty(-10.0000, "V")$ output jack], [4mm banana, blue], [Reference voltage output], [$plus qty(10.0000, "V")$ input jack], [4mm banana, white], [Reference voltage input], [$qty(-10.0000, "V")$ input jack], [4mm banana, white], [Reference voltage input], [AGND jack], [4mm banana, black], [Analog ground reference], [Dual $qty(10, "MHz")$ sine oscillator output jacks $plus.minus qty(1, "V")$], [4mm banana, light blue], [Master oscillator output (independent paths, to allow verification - see @the-time-invariant)], [$qty(10, "MHz")$ sine oscillator input jack], [4mm banana, white], [Master oscillator input], [Calibration coarse], [Rotary or DIP switch], [Reference voltage coarse adjust], [Calibration fine], [Rotary or DIP switch], [Reference voltage fine adjust], ), caption: [Chassis front panel elements], ) - Case designers may add other elements as they see fit (fuse holders, voltage selectors, sensors, etc.), - Reference jacks should be grouped together, on a $qty(0.75, "inch")$ grid, - All controls and jacks must have an associated label. === Electrical safety ==== Mains isolation #figure( table( columns: 2, table.header([Parameter], [Requirement]), [Isolation voltage], [$gt.eq qty(3000, "VAC")$ mains to SELV], [Creepage / Clearance], [Per IEC 60950-1 or IEC 62368-1], [Fusing], [Primary slide, appropriately rated], [Earth bonding], [Continuous, $lt qty(0.1, "ohm")$ to mains earth], ), caption: [Mains isolation requirements], ) ==== SELV circuits All module-facing voltages ($plus.minus qty(15, "V")$, $plus.minus qty(10, "V")$, $plus.minus qty(5, "V")$) are Safety Extra-Low Voltage (SELV): #figure( table( columns: 2, table.header([Parameter], [Requirement]), [Maximum voltage], [$lt qty(60, "VDC")$], [Isolation from mains], [Required], [User accessible], [Yes (banana jacks)], ), caption: [SELV circuits requirements], ) ==== Protective earth #figure( table( columns: 2, table.header([Parameter], [Requirement]), [Earth continuity], [$lt qty(0.1, "ohm")$ from any exposed metal to mains earth], [Earth current capacity], [Per fuse rating], [Chassis bonding], [All panels bond], ), caption: [Protective earth requirements], ) === Compliance Chassis must comply with applicable safety and EMS standards for the target market: #figure( table( columns: 3, table.header([Region], [Safety], [EMC]), [EU], [IEC 62368-1], [EN 55032, EN 55035], [USA], [UL 62368-1], [FCC Part 15], [International], [IEC 62368-1], [CISPR 32, CISPR 35], ), caption: [Chassis compliance requirements], ) Compliance testing and certification are the responsibility of the chassis manufacturer.